1. Field of the Invention
The present invention relates to a process for producing composite thermoplastic sheets and component parts by resin impregnation of glass fiber mats.
2. Description of Related Art
Currently used commercial equipment and processes for production of thermoplastic sheet blanks and shaped component parts formed from such blanks suffer from several disadvantages. One known example of such processing equipment, which employs stainless steel belts to effect conductive heating and cooling of the materials, is very expensive, requiring high capital costs, and is further limited by slow heating rates. Further, glass reinforced composite sheets made with such equipment evidence voids, primarily at the fiber/resin interfaces and in the resin matrix. These voids are the major type of imperfection found in such sheets.
Elimination of voids in sheets or component parts produced from resin-impregnated glass fibers is very important in improving the mechanical properties of the sheets or parts. Voids in these composites are detrimental to the integrity and strength of the composite because fiber-polymer interfacial or interstitial voids cannot transmit a transverse load. The voids also significantly weaken the longitudinal compressive strength and interlaminar shear strength of the material. For example, a void content of 5% between the fiber and resin reduces interlaminar shear strength by 30% and longitudinal compression strength by 50%.
Known processes and equipment also suffer from the limitation that they are generally capable of producing parts only from preimpregnated sheet blanks, which in conventional flow forming processes are required to be preheated. Additionally, the production of long profiled parts such as hollow beams, tubes, corrugated panels, and the like have heretofore been produced by a process known as pultrusion, wherein generally low viscosity resins and unidirectional fiber reinforcements must be employed.
It is therefore an object of the present invention to provide an improved process for impregnating glass fibers with resins to produce composite structures or parts.
It is another object of the present invention to provide a process for impregnating glass fibers with resins to produce composite structures or parts wherein capital costs of equipment are relatively low, and the process further provides energy efficiency in operation.
It is a further object of the present invention to provide a process for manufacture of fiberglass composites employing fast heating of the materials making up the composite structures or parts, further enabling lamination of materials having a high melting point or glass transition temperature.
It is a further object of the present invention to provide a process for impregnating glass fibers with resins wherein improved adhesion between the glass fibers and the resin is attained.